The invention relates to an inlet arrangement for an internal combustion engine.
It is known that combustion in an internal combustion engine can be improved by controlling turbulence within the combustion chamber of the fuel and air mixture immediately prior to combustion. A certain amount of turbulence can be created by causing the mixture to swirl around the axis of the combustion chamber (generally known as axial swirl). However such swirl does not lead to significant turbulence immediately prior to combustion.
Better turbulence characteristics can be obtained by inducing what is known as barrel swirl as illustrated in FIGS. 1, 2 and 3 of the accompanying drawings which are diagrammatic cross sections through a cylinder. In FIG. 1, a mixture of fuel and air has been induced into a cylinder 1 by a descending piston 2 and the incoming mixture follows a generally cylindrical path indicated by arrow A transverse the axis X of the combustion chamber. As the piston 2 ascends, compression of the mixture causes the cylindrical motion of the mixture to increase in speed as in FIG. 2 until eventually, as shown in FIG. 3, the swirling mixture breaks down into a large number of small eddies E immediately prior to combustion. Such barrel swirl provides a greatly improved turbulence of the air and fuel mixture immediately prior to combustion and is highly desirable. Such small eddies are known in the art as "micro turbulence". It has been found that an inlet port giving high barrel swirl provides good part throttle stability, fuel economy, lean burn limit and good idle stability. Such inlet ports are conveniently referred to as low flow/high swirl ports. It has also been found that where the inlet port is designed to enable a high rate of mixture to flow directly into the cylinder with zero or low induced barrel swirl, high specific power outputs can be achieved giving higher Kw/litre of engine capacity. Such inlet ports are conveniently referred to as high flow/low swirl ports.
An object of the present invention is to provide an inlet arrangement for an internal combustion engine which can achieve the advantages of both low flow/high swirl ports and high flow/low swirl ports.